The present invention relates to a screw adjusting apparatus for adjusting the position of, for example, a magnetic head of a video tape recorder promptly and precisely by moving the magnetic head with the end of a screw.
Conventionally, an adjustment for moving the magnetic head using a screw mechanism depends much on an operator's visual sense. Therefore, there is a growing demand for the development of an automated screw adjusting apparatus capable of performing its function promptly and precisely.
An example of a conventional automated screw adjusting apparatus for adjusting the position of a magnetic head clamped to the cylinder of a video tape recorder is described below.
FIG. 6 is a sectional view showing the principal portions of the head adjusting section which clamps a head base to the cylinder of the video tape recorder by moving a screw vertically.
Referring to FIG. 6, the head adjusting section comprises: a rotary cylinder 1; a head base 2 clamped to the rotary cylinder 1; a head tip 3 mounted on the head base 2; a screw 4 which clamps the head base 2 to the rotary cylinder 1; a screw 5 which presses the head base 2 downward and provides a clearance between the head base 2 and the cylinder 1; and a bit 6 for transmitting the rotation of a motor to the screw 5.
According to the above head adjusting section, the initial position of the head tip 3 with respect to the axial direction of the cylinder 1 is visually detected. If there is a difference between the initial position of the head tip 3 and the predetermined position, the screw 5 is rotated a certain angle by a motor in order to move the head base 2. Then, the position of the head tip 3 is visually detected again. This operation is repeated until the position of the head tip 3 with respect to the predetermined position is within the tolerance.
In addition, before the bit 6 is removed from the screw 5, it is necessary to rotate the bit 6 reversely less than the backlash so that the bit 6 can be smoothly removed from the screw 5. As a result, the screw 5 is released from the pressing force of the bit 6 and consequently, the position of the head tip 3, namely, the head base 2 is moved upward. This phenomenon is hereinafter referred to as "spring-back". Therefore, it is necessary to detect the position of the head tip 3 visually again. If the position of the head tip 3 with respect to the predetermined position is out of the tolerance, the operation for moving the head base 2 downward is repeatedly carried out.
According to this conventional method, since the adjustment amount of the head tip is slight, the rotational amount of the screw 5 per step is slight. If the clearance between the head base 2 and the cylinder 1 is great, many steps are required until the clearance between the head base 2 and the cylinder 1 is within the tolerance. Therefore, it takes much time to complete the positioning operation.
Further, according to the conventional method, it is difficult to rotate the screw 5 promptly because the spring-back amount of the head tip 3 is nonuniform. In the worst case, the screw 5 cannot be fed to the predetermined position.